Re: The 2e power supply

[Alex Freed <alexf@mirrow.com>]

Michael J. Mahon wrote:
> Alex Freed wrote:
>
> So the line-side supply is fine and stable, but the low voltages
> are out or regulation?  Or in regulation but at too low a set point?
> (Do they drop much when a load is applied?)
>
> Sounds like you have an unusual failure mode.  ;-)

Well, yes. The line-side supply is close to perfection.
Looks like the problem was a tiny 1 uF 35V cap. The pads under it
were corroded which could mean that the electrolite left the cap a while 
ago.
Remember that all electronic components run on smoke? When the smoke 
gets out they stop functioning. And electrolitics need liquid in 
addition to smoke to operate.
So I took it out and measured approximately 0 uF. Replaced by a fresh
1 uF and the device is much happier.

Probably blindly replacing the electrolitics is a good strategy unless 
something is clearly wrong on the board. I just didn't have 100 uF by 
200V caps in my junk box and Jameco is closed :)

As a side remark this particular supply uses a 7905 and 7912 for the
negative voltage low current linear  regulation. Which confirms what was 
written in a recent thread.

-Alex.